In some circumstances we can end up with setup costs that are very complex to
compute, even though the scevs are not very complex to create. This can also
lead to setupcosts that are calculated to be exactly -1, which LSR treats as an
invalid cost. This patch puts a limit on the recursion depth for setup cost to
prevent them taking too long.
Thanks to @reames for the report and test case.
Differential Revision: https://reviews.llvm.org/D60944
llvm-svn: 358958
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
In some loops, we end up generating loop induction variables that look like:
{(-1 * (zext i16 (%i0 * %i1) to i32))<nsw>,+,1}
As opposed to the simpler:
{(zext i16 (%i0 * %i1) to i32),+,-1}
i.e we count up from -limit to 0, not the simpler counting down from limit to
0. This is because the scores, as LSR calculates them, are the same and the
second is filtered in place of the first. We end up with a redundant SUB from 0
in the code.
This patch tries to make the calculation of the setup cost a little more
thoroughly, recursing into the scev members to better approximate the setup
required. The cost function for comparing LSR costs is:
return std::tie(C1.NumRegs, C1.AddRecCost, C1.NumIVMuls, C1.NumBaseAdds,
C1.ScaleCost, C1.ImmCost, C1.SetupCost) <
std::tie(C2.NumRegs, C2.AddRecCost, C2.NumIVMuls, C2.NumBaseAdds,
C2.ScaleCost, C2.ImmCost, C2.SetupCost);
So this will only alter results if none of the other variables turn out to be
different.
Differential Revision: https://reviews.llvm.org/D58770
llvm-svn: 355597
LSR reassociates constants as unfolded offsets when the constants fit as
immediate add operands, which currently prevents such constants from being
combined later with loop invariant registers.
This patch modifies GenerateCombinations() to generate a second formula which
includes the unfolded offset in the combined loop-invariant register.
This commit fixes a bug in the original patch (committed at r345114, reverted
at r345123).
Differential Revision: https://reviews.llvm.org/D51861
llvm-svn: 346390
Fangrui Song